X-ray Computed Tomography (CT) is the most widely used imaging modality for the diagnosis of various disease and disorders in animal and human population. Iodinated agents are routinely used as contrast enhancers to produce clinically intelligent images via X-ray CT. However, iodinated agents suffer from several drawbacks. One drawback is that the resolution of CT to detect cancer and other disorders within the body using iodinated agents at early stages of cancer development is limited by the inadequate contrast between the healthy and cancerous tissues. Another issue is that some patients develop allergic reactions as a result of administration of iodinated agents. Also, iodinated agents rapidly wash off clear from tissues, which impedes continuous monitoring of patients images through CT. Iodinated agents are also non specific, which prevents highly targeted imaging of specific tissue regions.
CT imaging uses special x-ray equipment to produce multiple images or pictures of the inside of the body and a computer to join them together in cross-sectional views of the area being studied. The images can then be examined on a computer monitor or printed. CT scans of internal organs, bone, soft tissue and blood vessels provide greater clarity than conventional x-ray exams. Because of its great sensitivity and specificity, CT scanning is often the preferred method for diagnosing many different cancers, including lung, liver and pancreatic cancer, since the image allows a physician to confirm the presence of a tumor and measure its size, precise location and the extent of the tumor's involvement with other nearby tissue. CT scans have also become pivotal medical diagnostic modality in examination that play a significant role in the detection, diagnosis and treatment of vascular diseases that can lead to stroke, kidney failure, and death.
Iodinated agents sometimes referred to as “dye”, which are liquids, are used as CT contrast enhancers to produce images of specific organs, blood vessels and/or tissue types “stand out” with more image contrast to better show the presence of disease or injury. Thus, CT contrast highlights specific areas of the resultant CT image. While iodinated agents have become ‘work horses’ of medical CT imaging modality, they suffer from the major disadvantages discussed above. In addition, the application of iodinated contrast agents is restricted in certain patients because of the impact of these agents on the renal function. With iodinated agents, some imaging studies are limited by the injected dose and the rate of dose injection.
Certain types of diseases including, cancers should be monitored via imaging for a long period of time. For example, over 25% of patients with colorectal cancer develop metastasis in liver within 2-4 months post surgery. However, there are no tumor markers for continuous staging of the metastasis in liver in patients after they have been operated for removal of colorectal tumors. Currently available iodinated agents for CT imaging are unsuitable as the contrast agent is not retained in the liver for a sufficient length of time. For these and other reasons, there is a considerable need for new contrast agents.